1. Technical Field
The present invention relates to an Arabidopsis AtLEJ1 gene which functions to inhibit the biosynthesis of the phytohormones jasmonic acid and ethylene. More particularly, the present invention relates to a male sterility-inducing gene that guarantees the security of a stable sterile line and requires no maintainers to maintain male sterility in the line. The present invention is also concerned with a male sterile, transgenic plant comprising the gene, which can be restored to a fertile phenotype by simple hormonal treatment, and to a method for producing the same.
2. Background Art
The development of new plant varieties is very important in view of securing foodstuff or being competitive in the floricultural industry of high-value plants, for example, roses and orchids, and intensive and extensive research on new plant varieties has been done in order to gain a competitive advantage. The development of novel plant varieties is accomplished, for the most part, through hybridization and gene manipulation.
In most cases, F1 hybrids between pure male and female lines are used for new plant varieties because they show heterosis. That is, generally, F1 hybrids outgrow their parents and bear more progeny, show more uniform properties and have shorter flowering and ripening time periods, thus being more tolerant of poor environments than their parents.
It is relatively easy to produce hybrid seeds from plants that have big flowers and many seeds per fruit, such as cucurbitae, because they are susceptible to artificial pollination. However, onions and carrots are difficult to artificially pollinate due to their small flowers. Only a small number of seeds can be obtained in one round of crossing, making it impractical to produce hybrids by artificial pollination. Furthermore, hermaphrodite plants require emasculation, which is labor-intensive, time-consuming work for removing maternal line stamens in flower buds, as a prerequisite to artificial crossing.
If there is a male-sterile line, females thereof may be used along with males from a normal fertile line. In this case, F1 hybrid seeds can be obtained through open pollination without emasculation. Thus, the development of male-sterile plants is very important for the development of new varieties. Male sterility is defined as the failure of plants to produce functional anthers, pollen, or male gametes, which is largely due to malformation of male flowers or anthers or defective anther dehiscence.
Male sterility can be achieved spontaneously or artificially via mutations in nuclear and/or cytoplasmic genes. Genetic mail sterility is expressed mainly as a survival disadvantage and shows a recessive inheritance pattern. Because sterility is obtained only in homozygously recessive alleles, a lot of effort must be made to maintain and proliferate the sterile line. As for plants with small flowers, their fertility is difficult to determine. Further, male sterility is difficult to apply to crops which need a long period of time for flowering.
In the meanwhile, the progeny of cytoplasmic male sterile plants would always be male sterile even if they are interbred with any fertile strain. Thus, the male sterile progeny must be crossed with various fertile strains to find individuals or lines that can produce 50% or 100% sterile strains, that is, maintainer lines. However, this is not practical. Artificial male sterility has been introduced through applying radiation or chemicals to male sterile lines for breeding F1 hybrids. Such radiation- or chemical-induced male sterility is so unstable that it is difficult to put into practice.
In spite of tremendous investment in the research and development of male sterile plants for the production of F1 hybrids, only modest results have been achieved due to the above-mentioned problems with male sterile plants. If the disadvantages with the male sterile plants could be circumvented, that is, if stable male sterile lines could be secured and maintained without other maintainer lines, they would be useful in the development of new varieties and in the industrial production of highly valuable plants.
Therefore, there has been a need for novel genes that allow for the stable male sterile lines without other maintainer lines.